1. Field of the Invention
The invention relates generally to rotary cutting tools and, more particularly, to drilling tools with a replaceable cutting insert. The invention also relates to cutting inserts and tool shanks for rotary cutting tools.
2. Background Information
The modern metalworking trade primarily uses twist drills to make borings. Depending on the application, these twist drills can differ in terms of their cutting material and geometry. Cutting materials traditionally used are increasingly being replaced by different types of cutting materials that have significantly higher resistance to abrasion. For relatively large drilling tools, however, a drill made entirely of such abrasion-resistant materials is generally too expensive, and is not economical in spite of its excellent cutting performance. Alternatives are twist drills in which a drill tip made of abrasion-resistant materials is permanently attached to a carrier tool that is generally made of cheaper, more traditional materials. The disadvantage of these tools, however, is that they can be repointed only to a limited extent. As soon as the relatively short cutting portion made of abrasion-resistant materials has been used up, the entire tool has to be scrapped.
To reduce overall costs and reduce or eliminate waste of material, it is advantageous to construct a drill with a replaceable cutting tip. Such replaceable cutting tips permit a user to replace the cutting tip when it is worn down without having to replace the entire drill. On drill bits of this type, a cutting head or insert is detachably fixed to a drill shaft either by a separate fastening mechanism or through structures on the insert and drill shank themselves that interact to retain the cutting insert in the shank and serve to transfer rotational forces from the shank to the insert. Such retention and rotation structures are subject to deformation and failure during service life due to concentration of stresses imposed during ordinary service. Such failures are undesirable, especially when involving a shank intended to be reused multiple times in conjunction with replaceable inserts.
There is, therefore, room for improvement in rotary cutting tools having replaceable cutting inserts, particularly in the shank members and replaceable cutting inserts therefor.